Maxima Special symbol
?As prefix to a function or variable name, ? signifies that the
name is a Lisp name, not a Maxima name.
For example, ?round signifies the Lisp function ROUND.
See Lisp and Maxima for more on this point.
The notation ? word (a question mark followed a word, separated by whitespace)
is equivalent to describe("word").
The question mark must occur at the beginning of an input line;
otherwise it is not recognized as a request for documentation.